1. Field of the Invention
The present invention relates to a polarizing plate including a hard coating film, and, more particularly, to a polarizing plate including a hard coating film which exhibits high hardness and superior physical properties.
This application claims the benefit of Korean Patent Application No. 10-2012-0097139, filed on Sep. 3, 2012, and Korean Patent Application No. 10-2013-0089106, filed on Jul. 26, 2013, which are all hereby incorporated by reference in their entireties into this application.
2. Description of the Related Art
A liquid crystal display (LCD) is one of a variety of flat panel displays which are currently widely available. Typically, an LCD is configured such that a liquid crystal layer is interposed between a thin film transistor (TFT) array substrate and a color filter substrate. When an electric field is applied to electrodes of the array substrate and the color filter substrate, liquid crystal molecules of the liquid crystal layer interposed therebetween are differently arranged, thereby displaying an image.
Meanwhile, a polarizing plate is provided outside the array substrate and the color filter substrate. The polarizing plate enables selective transmission of light in a specific direction among light from a backlight unit and light passed through the liquid crystal layer, thus controlling polarization.
The polarizing plate includes a polarizer for polarizing light in a predetermined direction and a protective film attached to the polarizer to support and protect the polarizer.
With the recent trend of manufacturing thin and slim display devices, attempts are being made to design a polarizing plate so as to externally expose the outermost layer of the polarizing plate. Upon manufacturing polarizing plates, poor quality polarizing plates may result from scratching, which undesirably increases defective rates of panels.
In order to achieve a film having high hardness and wear resistance, coating films for a hard coating layer are proposed. An increase in surface hardness of the hard coating layer involves an increase in the thickness of the hard coating layer. However, a thicker hard coating layer, although increasing the surface hardness, is more prone to setting shrinkage which leads to wrinkling or curling with the concomitant production of cracks or exfoliations, and thus thick hard coating layers are difficult to employ in practice.
Recently, several methods have been proposed for conferring high hardness on hard coating films, without the problems of cracking and setting shrinkage-induced curling.
Korean Patent Application Publication No. 2010-0041992 discloses a composition for a hard coating film using a binder resin including a UV curable polyurethane acrylate oligomer, without the use of a monomer. However, this hard coating film has a pencil hardness of about 3H and thus has insufficient strength.
Also, formation of a hard coating layer having a thickness of 20 μm or more is devised to enhance pencil hardness on a plastic substrate. Although the hard coating film thus obtained is improved in hardness, it has poor impact resistance and thus may crack or break even under low impact, and may severely curl during the manufacture process, making it difficult to manufacture, by conventional techniques, hard coating films having high hardness with good physical properties. Hence, the development of a useful hard coating film having high hardness and impact resistance is required.